Superfluid $^3$He in Anistropic Aerogels

Anisotropic quasiparticle scattering has been predicted to modify the properties of superfluid $^3$He in high porosity silica aerogels.\footnote{K. Aoyama and R. Ikeda, Phys. Rev. B {\bf73}, 060504(R) (2006).} For example, anisotropic scattering produced by axial compression (or elongation) of the aerogel has been predicted to stabilize the axial (or polar) state of superfluid $^3$He. We have used a transverse acoustic impedance method to determine the phase diagram of superfluid $^3$He in a 98\% porous silica aerogel subjected to 17\% axial compression. We have found that this uniform axial anisotropy does not increase the stable region of A-like phase but does inhibit the nucleation of the B-phase at low pressure. We have performed optical cross-polarization experiments\footnote{J. Pollanen {\emph{et al.}}, J. of Non-Crystalline Solids {\bf354}, 4668 (2008).} to verify the presence and uniformity of the anisotropy in the aerogel samples. Additionally, we are performing nuclear magnetic resonance experiments on superfluid $^3$He in aerogels with anisotropy introduced with either axial or radial compression.